This invention relates to the measurement of the volume of small particles and the volume distribution of small particles. More particularly, the invention relates to the use of 90.degree. scattering in the measurement of the volume of small particles in the range of approximately 0.1 to 10 microns in diameter, for example. In the past, there has been no reasonably accurate and simple method of determining the volume of small particles which include particles in the submicron region. This is particularly true with regard to the real time measurement of such particles which has become a necessity with the ever-increasing importance of real time measurement of particulate size in source emissions particularly in the size range from 0.1 to 10 microns in diameter. It is therefore an object of this invention to provide a method for making accurate measurements of the volume of small suspended particles and particularly a method of determining the volume distribution of small fluid suspended particles in different size ranges so as to be able to construct a histogram therefrom.